Introduction Degenerative musculoskeletal conditions such as osteoarthritis and rotator cuff tendinopathy show increased incidence with age. The aim of this study was to evaluate a number of tissue characteristics associated with rotator cuff tendinopathy and ageing in samples of human supraspinatus tendon from individuals over a wide age range.
Methods Patients attending our shoulder clinic for treatment of traumatic shoulder instability or rotator cuff pathology were recruited to the study and tissue samples were obtained at the time of outpatient or surgical treatment. Participants were categorised by age into six groups: under 35, 35–44, 45–54, 55–64, 65–74 and 75 years and over.
Samples were taken under ultrasound guidance from the supraspinatus tendon. The biopsies were obtained in clinic under local anaesthetic for the injection group and in the operating theatre for the surgical and control groups. The tissue samples were wax embedded, sectioned and stained using the following markers: H&E to assess cellularity; CD34 to identify vascular endothelial tissue; MIB-1 to identify proliferating cells; Active Caspase-3 to identify cells undergoing apoptosis; SIRT-1 as a marker of ageing.
Results Table 1 details the composition of the age groups. The immuno histochemical results (figure 1) show a comparison of tissue characteristics evaluated across the spectrum of age. No significant change in cellularity was seen between the groups. Vascularity (CD34) of the supraspinatus tissue showed a significant reduction with age, showing a rapid decline in vascularity from 55 years of age onwards. A similar pattern of expression was seen for proliferation (MIB-1) with the major decline in proliferative activity occurring between 55 and 65 years. Cellular apoptosis (Active Caspase-3) showed a decline in the older age groups although this only reached significance in the 65–74 year old age group. SIRT-1 as a potential marker of tissue ageing showed a declining trend across the age groups with significant reduction in expression seen in the two oldest age groups.
Discussion The results demonstrate significant changes in several major features of tissue activity and viability within the supraspinatus tendon as age increases. Once age reached 55 years and over, the tissue demonstrated significant reductions in cellular activity and potential viability matching with the peak age of onset of rotator cuff pathology. SIRT-1 showed a constant gradual decline in expression as age increased, in keeping with the existing theories that reduction of SIRT-1 activity may be associated with cell senescence and ageing.
The study was limited by the recruitment of tissue samples from a population attending for hospital treatment. The results may include some bias associated with pathological tissue changes unrelated to the patients' age. Despite this limitation, however, this work has shown a clear and significant pattern of tissue change associated with increasing age in the population studied and will lead to future work employing similar methods to investigate the tissue changes seen in a healthy ageing population.